For better wear resistance of cutting tools, hard coatings such as TiN, TiCN, and TiAlN coatings are applied onto substrates of the cutting tools. The substrates are exemplified by those made typically of hard metals, cermets, and high-speed tool steels. However, further demands have been made to provide hard coatings with still better wear resistance with increasing hardness of workpieces to be cut or increasing speed of cutting operation.
Such hard coatings with excellent wear resistance are exemplified by hard coatings including oxides (oxide hard coatings). Typically, in Patent literature (PTL) 1, the applicant (assignee) of the present application proposes a coating having better wear resistance as compared with the conventional TiAlN coatings and oxide coatings. This coating includes (Ti, Al, Si)O in a predetermined compositional ratio. However, demands have still been made to provide a hard coating having better chemical stability at high ambient temperatures and having better wear resistance.